The present invention relates generally to mechanisms for protecting mechanical drive components from overloads, and more particularly relates to a shear device coupled between components of an agricultural disc mower that protects the various components of the mower in the event a cutterhead strikes an object and creates an overload condition in the driveline.
Typical disc cutterbars used in agriculture include an elongated housing containing a train of meshed idler and drive spur gears, or a main power shaft or a series of shafts coupled by respective bevel gear sets, for delivering power to respective drive shafts for cutterheads spaced along the length of the cutterbar. The cutterheads each comprise a cutting disc including diametrically opposed cutting blades (though configurations with three or more blades are known) and having a hub coupled to an upper end of a drive shaft, the lower end of the drive shaft carrying a spur gear in the case where a train of meshed spur gears is used for delivering power, and carrying a bevel gear of a given one of the bevel gear sets in the case where a main power shaft is used. In either case, as would be expected, bearings are used to support the various shafts. The cutterheads are rotated at a relatively fast speed making the drive components, such as gears, bearings, and shafts vulnerable to damage in the event that the unit strikes a foreign object.
In order to minimize the extent of such possible damage to the drive components, it is known to incorporate a shear device somewhere in the drive of each unit which will “fail” upon a predetermined overload being imposed on the device. As used herein with reference to shear devices, the terms “fail” or “failing” are intended to cover the actual function of such devices, i.e., shearing, fracturing, breaking and the like.
One known type of shear mechanism employs frangible splines engaged on an interfacing splined shaft. The shear device is in the form of either a collar or clamping member having internal splines received on a splined end of the drive shaft. An overload situation preferably causes the splines in the shear device to shear and the continuing transfer of rotational power to cease. Variation of the overload situation (shear torque) at which the internal splines shear is accomplished through variation in the number, profile (height), length, or material of the splines. Such means often lack the precision necessary to achieve the desired shear torque needed for optimal rotary cutter shock protection or cause other operational problems when a low shear torque threshold is required. For example, use of spline length as a means for shear torque variation can result in a shock hub that is unstable when mounted on a shaft due to insufficient spline engagement length. Variations in the number of splines increase production costs as unique tooling may be necessary to provide the desired variations.
It would be advantageous to have a driveline shock protection device having improved capability to precisely establish a pre-determined shear torque value without compromising the operation or production cost of a driveline shock hub that overcomes the above problems and limitations.